(1) Field of the Invention
The present invention relates to a substrate for print circuit board, a print circuit board and methods of manufacturing the same. More particularly, the invention relates to a substrate for print circuit board and a print circuit board which are excellent in mechanical and thermal characteristics and smoothness, and manufacturing methods thereof.
(2) Description of the Prior Art
With the development of electronic materials such as IC, LSI, power transistors and the like, there have recently been developed various print circuit boards. The print circuit boards are ordinarily classified into the hard print circuit boards mainly consisting of phenols, epoxy, and composite, and the flexible print circuit boards featured by their flexibility. However, the flexible print circuit boards have the drawbacks that they are still costly at present and difficult to use.
It is the recent trend that further miniaturization, densification and intensification of materials for electronics are demanded, the capacity becomes larger and the tip size are increased. It has become an important problem how to dissipate the heat generated from electronic parts and electronic circuits with the intensification and the large capacity. In order to resolve such a problem, there has been developed a so-called metal core print circuit board in which a metal sheet is used as a core. Particularly, there has recently been studied a method of constituting print circuit boards by using enamel steel sheets, which are disclosed, for instance, in Japanese Patent Laid Open Nos. 3,673/1981, 62,389/1981, 88,344/1981, 10,994/1982 and so on. The print ciruit boards using such enamel steel sheets have the merits that they are not only excellent in the mechanical and thermal characteristics but also they can be processed into any arbitrary profile prior to firing of the enamel.
However, the conventional IC and LSI circuit boards using the enamel steel sheet are subjected to the firing after the electroconductive or electric resistant ink is directly applied to print the enamel film layer, and often problems occur that the adhesion of the print circuit board is lowered due to the firing treatment at a high temperature, which may ultimately cause the peeling-off.
When the enamel of such a small thermal expansion coefficient as to meet that of the LSI tip or a conductive ink is used to avoid the above-mentioned drawbacks, there is a problem that excellent adhesion to the base steel sheet cannot be obtained. In view of the present situation that in the case of the print circuit board using the enamel steel sheet, the heat dissipation and the heat expansion are still unsatisfactory in addition to the above-mentioned drawbacks in the production of the recent IC and LSI print circuit boards, the appearance of a print circuit board which is fundamentally improved has been expected.